1. Field of the Invention
The present invention relates to a miniature portable equipment having a specified packing, particularly a wristwatch having a specified packing or miniature portable information equipment terminal having a specified packing. More particularly, the present invention relates to a wristwatch of long-life specification wherein use is made of, for example, a long-life battery or a solar cell energized by conversion of light to electrical energy, or of mechanical specification wherein no battery is needed, or of specification wherein washing can be effected by the use of, for example, an ultrasonic cleaner, which wristwatch is fitted with a packing capable of inhibiting the penetration of water and steam from outside and also the penetration of human sweat and sebaceous matter, etc. and hence being excellent in long-term waterproofness.
2. Description of the Prior Art
It is demanded for miniature portable equipments, a representative example of which is a wristwatch, to be waterproof because these are daily worn.
For example, referring to FIG. 4 which shows a partial section of a wristwatch exterior component, ring-shaped waterproof rubber packings are disposed at seal portions of the wristwatch exterior component, namely, interstice between wristwatch case main body 4 and back lid 7, interstice between the case main body 4 and windshield glass 2, portion of stem 6, portion of push button, etc. With respect to the packings shown in FIG. 4, packing 3 is generally called “windshield glass packing”, packing 5 as “stem O-ring”, and packing 1 as “back lid O-ring”. FIG. 5 shows a section from which the outline of waterproof structure for the interstice between wristwatch case main body 4 and back lid 7 is apparent. This waterproof structure is constituted of a ring-shaped elastic back lid O-ring 1 fitted in compressed condition in a concave groove formed in the back lid 7. The penetration of water from outside is inhibited, and the waterproofness for wristwatch internal parts is ensured, by compressing the back lid O-ring 1 into contact with the case main body 4 and the back lid 7 and maintaining an appropriate contact stress.
Moreover, for example, referring to FIG. 6 which is a partial sectional view of conventional wristwatch structure, stem pipe 13 is secured to wristwatch case 11, and stem 12 has ring-shaped groove 18 provided on stem shaft portion 17. Waterproof packing 15 is fitted in the ring-shaped groove 18. For time resetting, winding stem 16 is coupled with the stem shaft portion 17. In this structure, the stem shaft portion 17 of the stem 2 oscillates inside the stem pipe 13 with the waterproof packing 15 interposed therebetween. The waterproofness for the wristwatch case 11 is ensured by the waterproof packing 15 compressed into contact with the inner wall surface of stem pipe 13.
With respect to the above waterproof packing for use in the wristwatch exterior component, from the viewpoint of long-term durability of packing waterproofness, it is demanded that the packing per se be nonpermeable to water and moisture, and further that the penetration of water from the above compressed contact part do not occur, accordingly, the packing in compressed contact condition exhibits long-term wear resistance and low compression set properties.
It is common to use, as a material for the above waterproof packing, for example, a nitrile rubber which is an acrylonitrile-butadiene copolymer (hereinafter referred to as “NBR rubber”), a butyl rubber which is an isobutylene-isoprene copolymer (hereinafter referred to as “IIR rubber”) or an ethylenepropylene rubber which is an ethylene-propylene-diene terpolymer (hereinafter referred to as “EPDM rubber) in accordance with a demanded specification.
However, in the above conventional method, in the use of NBR rubber as the waterproof rubber packing material, although ensuring excellent resistance to oil and wear, the NBR rubber has a drawback in that not only the water ad moisture permeabilities but also the compression set.
In the use of IIR rubber, although ensuring excellent nonpermeability to water and moisture, the IIR rubber has a drawback in that not only is the wear resistance poor but also the compression set is large.
Also, in the use of EPDM rubber, although ensuring excellent nonpermeability to water and moisture, the EPDM rubber has a drawback in that not only is the wear resistance poor but also the compression set is large.
That is, with respect to the conventional packings of synthetic rubber materials, it is difficult to satisfy both the nonpermeability to water and moisture and the low compression set, and these synthetic rubber materials have posed a problem in compression set.
Therefore, with respect to conventional wristwatches having packings constituted of the above materials, when a compressive force is exerted thereon for a prolonged period of time, the packings would suffer a plastic deformation. Thus, an appropriate contact stress cannot be maintained, so that a gap would occur at waterproof seal portions. As a result, it has been impracticable to maintain waterproof and moisture proof performance. In particular, with respect to a wristwatch of long-life specification including a movement (module) wherein use is made of, for example, a long-life battery or a solar cell energized by conversion of light to electrical energy, or a wristwatch of mechanical specification, only replacement of waterproof rubber packings must be inevitably carried out every two to three years although battery replacement is not needed to thereby fail to realize a maintenance-free wristwatch. Furthermore, there has been a problem such that waterproof failure may be brought about by washing of a wristwatch by means of an ultrasonic cleaner or the like.
Description will be made in greater detail with reference to the partial sectional view of wristwatch shown in FIG. 6.
Generally, the stem 12 inserted in the stem pipe 13 is likely to be rickety in the direction perpendicular to axial direction as much as a distance corresponding to the interstice between the circumferential surface of stem shaft portion 17 and the inner wall surface of stem pipe 13. Also, the stem 12 is likely to be rickety between the circumferential surface of stem pipe 13 and the inner wall surface of stem collar portion 14 as much as the interstice therebetween. In the use of wristwatches for a prolonged period of time, it would occur that conventional waterproof packings 15 are deteriorated per se and deformed by the deterioration of packings by influences from outside dust and human sweat with the result that the compressive contact force on the inner wall surface of stem pipe 13 is unfavorably reduced.
When a large external force, for example, one resulting from collision of a matter upon the stem 12 in water, is applied to the stem 12 provided with the waterproof packing 15 whose compressive contact force has been reduced, the stem shaft portion 17 would suffer a move interlocked with the ricketiness of the stem 12. Thus, the state of uniform compressed contact of waterproof packing 15 would be highly likely to collapse with the result that the waterproof packing 15 would be set aside. Therefore, there has been a problem such that water penetration is likely to occur at portions where the compressed contact of waterproof packing 15 has been weakened. Furthermore, when the waterproof packing is deformed, the deformation may cause such a problem that, at the rotation of stem and at the oscillation inside the stem pipe, the move would be heavy.
The present invention has been made with a view toward solving the above technological problems of the related art. Therefore, it is an object of the present invention to provide a miniature portable equipment such as a wristwatch or miniature portable information equipment terminal fitted with a packing which is excellent in not only nonpermeability to water and moisture but also compression set performance and which, even when used for long, exhibits only a slight plastic deformation to thereby ensure excellent durability. Further, with respect to wristwatches of long-life movement (module) specification, a particular object of the present invention is to provide a maintenance-free wristwatch or a wristwatch of specification wherein washing can be effected by the use of, for example, an ultrasonic cleaner.